In the right-hand corner of the little cavern, five or six feet above my head, was a dark hole, like the entrance to a tunnel, or, more properly speaking, a good-sized burrow—­for it was scarcely more than a yard in diameter.  It seemed to be something more than a mere cavity in the rock, for, when I flashed my lantern up to it, I could see no end.  To climb up to it, at first, seemed difficult; but providentially, I had a stout claspknife in my pocket, and with this I cut a step or two in the porous rock, and so managed it.  Lying flat on my stomach, I looked in.

It was, as I had thought, a narrow natural tunnel, snaking through the rocks—­as often happens in those curious fantastic coral formations—­for all the world, indeed, as if it had been made ages ago by some monstrous primeval serpent, a giant worm-hole no less, leading—­Heaven alone knew where.

There was just room to crawl along it on all fours, so I started cautiously, making sure I had my precious matches, and my jackknife all safe.

After all, I said to myself, I was no worse off than thousands of poor devils in mines.  I had myself snaked through just such passages in coal-mines.  Still, I confess that the choking sense of being shut in this earth-smelling tube, like a fox in a drain, and the sudden realisation of the appalling tonnage of superincumbent earth above me—­liable at any moment to loosen, and, as with a giant thumb, press out my poor little insect existence—­made the sweat pour from me and my heart stand still.  I had to shut my eyes for a moment and command myself back to calmness and courage, before I could go on.  Above all things I had to blindfold my imagination, the last companion for such a situation.

After this first flurry of fear, I went on crawling in a methodical way, allowing no thought to enter my mind that did not concern the yard or two of earth immediately ahead of me.  So I progressed, I should say, for some twenty or thirty yards when, to my inexpressible relief, I came out, still on all fours, onto a spreading floor; then, standing up, I perceived that I was in a cave of considerable loftiness, and some forty feet or so across.  It was good to breathe again such comparatively free air; yet, as I looked about and made the circuit of the walls, I saw that I had but exchanged one prison for another.  There was this difference, however:  whereas there had only been one passageway from the cave I had just left, there were several similar outlets from that in which I now stood.  Two or three of them proved to be nothing but alcoves that ran a few yards and then stopped.

But there were two close by each other which seemed to continue on.  There was not much choice between them, but, as both made in the same direction, as far as I could judge the direction in which I had so far progressed, I decided to take the larger one.  It proved to be a passage much like the tunnel I had already traversed, only a little roomier, and therefore it was easier going, and it, too, brought me out, as had the other, on another cavern—­but one considerably larger in extent.